[Don Pensack]

Originally Posted by stonius

i'm surprised to hear you say that. I haven't noticed this in any of my scopes, and i notice some of gear is broadly comparable. Sure the xw's have some field curvature, as all eyepieces do, but it's been below the threshold of detection for me. I'm much more bothered by chromatic distortion, atmospheric refraction, or even the barrel distortion in my tv pan24 (but that's another story - just don't pan with the pan!).

The 24mm panoptic doesn't have barrel distortion (negative rectilinear distortion), it has pincushion distortion (positive rectilinear distortion).
Barrel distortion bends lines like this as they cross the field: ( | ),
whereas pincushion distortion bends the lines like this: ) | (.
Otherwise, i agree about quick panning across a field when the rectilinear distortion has a high %.

Can i ask if its worse with certain scopes? Supposedly they're designed with refractors in mind, so i wonder if it becomes more of an issue on very fast dobs (mine is f5).

There is no reason to think these 85° eyepieces were designed for refractor use. The market for the eyepieces will be mostly reflectors and the first focal lengths in the series have been chosen with reflector focal lengths in mind. Few refractors are designed with focal lengths longer than 1000mm these days, where 1500-2500mm focal lengths are fairly common in reflectors.

It's strange though as the xw40-14mm supposedly have positive curvature, and xw10 and above have negative curvature, so you would expect whatever field curvature issues you had to resolve either in the 14 or the 10mm as they have opposite curvature from each other.

That would depend on the field curvature in the scope.

Just strange how we can have such different experiences with the same eps.

Observers' abilities to accommodate field curvature varies from person to person and diminishes with age. So it's not surprising some see none and others see a lot with the same eyepiece. And refractors inherently have more fc than reflectors, so if the curves of scope and eyepiece don't match, you can get some objectionable results.



Cheers,
markus

see my notes above.